The present invention relates to the attachment of the bicycle wheel to the bicycle frame, more specifically the attachment of the rear bicycle wheel to the drive sprockets in conjunction with the attachment to the frame.
Heretofore, the complete rear drive sprocket assembly is assembled to remain affixed to the rear wheel hub. Thus the rear drive sprocket or sprockets remain attached to the rear wheel when the rear wheel is removed from the frame. Whenever the wheel or tire is damaged, or when the bicycle must be taken apart for transport, the wheel must be removed from the frame. Such an operation is likely to be required rather frequently.
Since the chain remains with the bicycle frame when the wheel is removed, it is no longer under the tension normally supplied by the wheel sprocket. The chain now tends to dangle and drag on the ground, picking up contaminants and spreading grease onto the surfaces that it comes in contact with. The lack of chain tension also causes it to fall off of the front sprockets and become tangled.
Reassembly of the wheel to the frame is also problematic, requiring a great degree of skill and dexterity. As the wheel is assembled to the bicycle frame, the operator must insure that the chain is properly guided through a series of sprockets and pulleys associated with the rear sprockets, the front chainwheel and the rear derailleur. Further, the present state of the art involves a rear sprocket assembly with as many as nine sprockets, each selectable via the rear derailleur. Upon reassembly of the rear wheel, the operator must insure that the derailleur is set to the outermost sprocket and that the chain is wrapped around this specific sprocket and also insure that the chain has not inadvertently become disengaged from any of the other sprockets in the drivetrain. This is often a daunting and messy task for most cyclists. While removal of the bicycle front wheel is a relatively easy operation that may be contemplated by the novice cyclist, removal of the rear wheel is considered to be an intimidating procedure better left to the professional or an enthusiast more fluent in the mechanics of the bicycle.
The rear wheel sprockets are commonly mounted to the conventional rear hub through a xe2x80x9cfreewheelxe2x80x9d subassembly where the sprockets are mounted to a one-way clutch, which is then threaded onto a collar of the rear hub shell. The current state of the art involves a variation on this design and is termed a xe2x80x9cfreehubxe2x80x9d, where the one-way clutch has a splined outer shell that is semi-permanently assembled to the rear hub. This clutch subassembly in commonly referred to as a freehub body. The individual sprockets are then slid over this splined shell to complete the rear hub assembly. Further description will focus on the freehub type of arrangement although the present invention is easily adaptable to the freewheel configuration or to any other arrangement with similar function, including a sprocket assembly that is fixed directly to the hub without a clutch.
The present invention involves a decoupling engagement mechanism between the one-way clutch assembly of the freehub, commonly referred to as the freehub body, and the rear hub shell, which is the outer rotating member of the rear hub. Thus, when the rear hub is removed from the bicycle frame, the freehub body, and its associated sprockets, remain attached to the frame. With the sprockets still in place, the chain remains under tension with the rear wheel removed. Thus, all of the problems associated with the dangling chain and the complex reassembly are eliminated. This greatly reduces the difficulty involved in replacement of the rear wheel and also solves the shortcomings previously described that are associated with the conventional hub assembly.
In the ensuing descriptions, the term xe2x80x9caxialxe2x80x9d refers to a direction parallel to the centerline of the wheel axle and the term xe2x80x9cradialxe2x80x9d refers to a direction perpendicular to the centerline of the wheel axle.
It should be recognized firstly that the freehub body must be coupled to the hub shell to transmit torque to the rear hub and secondly that the rear hub is mounted to the frame at the two exposed ends of its stationary axle. Thus, the wheel is commonly assembled to the bicycle frame in a generally radial direction with the axle ends residing in slots within the flattened portions of the frame commonly referred to as dropouts. These dropouts generally have a fixed distance of separation, leaving a predefined axial width assigned to the rear hub.
While the notion of such a decoupled sprocket arrangement is not new, most torque coupling arrangements require some degree of axial interference or overlap between the driving and driven elements in order to transmit torque. Previous designs required that the bicycle frame must be flexed and the dropouts spread so that the mating splines between the hub and the drive sprockets become disengaged to facilitate removal of the wheel. Such an arrangement adds difficulty to the procedure of disassembly of the wheel from the frame and leaves the frame vulnerable to overstress in this spreading process. These designs date back to the 1930""s and 1940""s and never saw any widespread use. Furthermore, modern bicycle frames, particularly with the advent of the mountain bike, are now constructed of much stiffer frame members that would render such a frame flexing procedure highly impractical, if not impossible.
More specifically, the present invention relates to a movable torque coupling element between the bicycle hub and the freehub body. The desired arrangement is that the sprockets are affixed to the freehub body and the freehub body is pivotally fixed to one dropout of the frame, preferably the right or xe2x80x9cdrive-sidexe2x80x9d dropout. Then the rear wheel, including the rear wheel hub, would be fitted between the right face of the left dropout and the left side of the freehub body. A torque coupling is then moved to engage the rear hub shell with the freehub body, allowing normal transmission of torque between the drive sprockets and the rear wheel. Thus, the movable torque coupling allows the overall axial width of the hub to collapse and be reduced, to the extent that it permits easy assembly and disassembly of the wheel to the bicycle frame without necessitating spread of the dropouts. The moveable torque coupling is then shifted into engagement with the freehub body, allowing the transfer of torque to the rear hub. In any transmission of torque, there is a driving element and a driven element. Since power is transmitted from the rider through the sprockets, the freehub body would be considered as the driving element and the rear hub, which applies the torque to the tire, would be considered the driven element.
Such a movable torque coupling may be designed to function in a variety ways. The torque coupling may be a passive element, for example one which is spring loaded, allowing the torque coupling to retract out of engagement during disassembly or reassembly of the rear wheel to the frame. Upon assembly of the rear wheel to the frame, the coupling element would be urged by the spring to snap into engagement with the freehub body and couple the transmission of torque between the sprocket and the wheel. One example of such an arrangement is illustrated in FIG. 6.
Alternatively, the torque coupling may be actively displaced or pushed into the engaged and/or disengaged position by any number of means. An example of such active torque coupling displacement is illustrated in FIGS. 1a-d where the torque coupling element is selectively manipulated and moved into an engaged or a disengaged position by a control shaft. In the engaged position, the freehub body is coupled to the rear hub to transmit torque, and in the disengaged position, the freehub body is uncoupled from the rear hub to allow wheel removal from the bicycle frame. Such an active torque coupling element may be manipulated by any combination of mechanical or electromechanical means including, but not limited to, cams, levers, shuttles, latches, etc.
While most discussion throughout this disclosure focuses on bi-directional torque coupling, where torque is transmitted from one element to another to drive, or be capable of driving, in both clockwise and counterclockwise rotating directions, it is also envisioned that such a torque coupling may be configured to transmit torque in only one direction of rotation and allow a freewheeling decoupling of the two members in the opposite direction of rotation. Thus, as shown in FIG. 6, it is feasible to incorporate the one-way clutch mechanism within the torque coupling itself, replacing the clutch mechanism normally located within the freehub body.